1. Field of the Invention
The present invention relates a noise preventing split ferrite core for a flat cable which is used to suppress not only noise conducting through the flat cable but also noise radiating therefrom and a noise preventing component, a wiring harness and an electronic apparatus which adopt therein the same noise preventing split ferrite core.
2. Description of the Related Art
Conventionally, in order to prevent noise from various types of electronic apparatus, for example, personal computers, a ferrite core is mounted on a cable connecting electronic apparatus. There are cables of various configurations and a flat cable is one of them. A ferrite core is, of course, mounted on such a flat cable for prevention of noise therefrom.
As a ferrite core for noise prevention from a flat cable, a ferrite core 1 shown in FIG. 12 has been used for that purpose and the ferrite core 1 has an inside diameter (or an inner sectional configuration) having a flat O-shaped (or a flat ring-like) configuration which corresponds to the outside diameter (or the outer sectional configuration) of a flat cable FC.
Moreover, a split ferrite core shown in FIG. 13 has also been used to facilitate attachment to and detachment from a flat cable. In this case, the ferrite core 1 is constructed such that the flat cable FC is held between split ferrite core bodies 1a, 1b which are abutted against each other.
A ferrite core attached to a flat cable needs to be fixed at an attached position such that the ferrite core does not move along the flat cable. This is because, if a ferrite core moves over a flat cable in an electronic apparatus after it is attached to the flat cable, the ferrite core comes into collision with a housing or component of the apparatus that is located adjacent thereto, this possibly leading to a failure of the ferrite core or a failure inside the electronic apparatus. In addition, the noise eliminating effect of the ferrite core differs depending on its position on the flat cable and therefore a change in the position of the ferrite core on the flat cable may affect the noise eliminating effect of the ferrite core. Thus, an optimum noise eliminating effect may not be obtained when the ferrite core moves over the flat cable.
As methods for fixing the ferrite core on the flat cable that have been used heretofore, in some cases the ferrite core and the flat cable are fixed to each other with an adhesive, an adhesive tape or the like, while in other cases the ferrite core is fixed to the housing of the electronic apparatus or on a substrate of the electronic apparatus which are located in proximity thereto.
However, these methods require labor hours. In particular, when an adhesive is used, a certain length of time is required before it sets up, and the ferrite core needs to be held at a position where it should be fixed until the adhesive is solidified. Thus, this method is disadvantageous in that a long production lead time is required. Moreover, with this method using an adhesive, if the ferrite core happens to be required to be removed for some reason, for instance, due to occurrence of a failure or defect in the ferrite core after it is fixed or occurrence of a disconnection of or defect in the flat cable, the ferrite core cannot be detached after the set adhesive is first removed and such work requires an extremely great deal of labor hours. In particular, where the flat cable and the ferrite core are secured to each other with an adhesive, there may be caused a failure in the coating of the flat cable or a disconnection of the flat cable while the adhesive is being removed, and if this happens, there may be caused a risk of the ferrite core and the flat cable being discarded.
With a view to overcoming a drawback as described above, components as shown in FIG. 14 are proposed for fixing the ferrite core (produced by TOKIN under a trade name of FPD-CL-1 Camp) of an integral-type. This component 5 is characterized in that it is attached to end surfaces of end portions of a ferrite core 1, respectively, and that it can be fixed onto an electronic apparatus housing or a substrate 10 with a screw 7 and a nut 8 using a hole 6 formed in the component 5.
However, workability in attaching the ferrite core 5 to the electronic apparatus housing or the substrate 10 with the screw 7 and the nut 8 is not necessarily good. For instance, when trying to attach the ferrite core 1 to the electronic apparatus housing or the substrate 10 with the components 5, first of all, the components 5 are mounted on the ferrite core 1, and thereafter the ferrite core is fixed to the housing or the substrate 10 while the components 5 have to be held in the mounted positions by hand so that they should not come off the ferrite core. In addition, where the ferrite core 1 is removed after it has once been fixed in place, the ferrite core 1 cannot be removed before the whole set of the core and components are detached from the substrate. Moreover, since the ferrite core 1 used together with the components 5 is of an integral type, the ferrite core 1 has to be attached to a flat cable FC before a connection of the flat cable FC is completed, in other words, for instance, before a terminal is connected to the flat cable FC or the flat cable FC is connected to the electronic apparatus, and even if the ferrite core or the flat cable so attached has to be replaced for some reason, for instance, due to a failure or a defect in the ferrite core or a disconnection or a defect of the flat cable, the ferrite core or the flat cable cannot be replaced with ease, thus the working efficiency being deteriorated.
On the contrary, in the case of a split ferrite core, the ferrite core can be attached to the flat cable in any stage. In addition, the core can be detached from the cable with ease due to the construction of the split ferrite core. However, as with the integral-type ferrite core, if the fixing method is used in which an adhesive or an adhesive tape is used as a fixing means, there are caused the same problems as those inherent in the integral-type ferrite core.
With a view to overcoming the above drawback, a component as shown in FIGS. 15 and 16 is proposed (produced by Kitagawa Kogyo under a trade name of EFC-40-N/S, disclosed on page 14 of the xe2x80x9cEMI Preventing Ferrite Technical Informationxe2x80x9d) for split ferrite core. This component 15 is characterized in that a case 16 is provided with a function to cover a ferrite core 1 by split ferrite core bodies 1a, 1b which are abutted against each other.
However, provision of such a function to the case 16 ends in a complicated construction and higher costs. In addition, since the inside diameter of the split ferrite core bodies 1a, 1b cannot be varied, it is not possible to hold the flat cable between the split ferrite core bodies 1a, 1b so securely that the ferrite core is not allowed to move thereover; therefore, a bottom of the component 15 needs to be fixed to an electronic apparatus housing or a substrate with a tape with adhesives on both sides or an adhesive.
Furthermore, in the case of conventional integral-type or split ferrite cores, they are selected such that the inside diameter (or the inner sectional configuration) thereof matches the dimensions of a flat cable inserted thereinto. The ferrite core can provide a better noise eliminating effect as the impedance value becomes higher which is obtained when the flat cable is inserted through the ferrite core, and the magnitude of impedance is determined by the magnetic permeability and configuration of a material for the ferrite core. With the magnetic permeability of the material for the ferrite core remaining constant, an impedance value obtained is in proportion to the effective sectional area of the ferrite core and is in inverse proportion to the length of an effective magnetic path. Therefore, it is desirable to select a ferrite core having a configuration which can provide as wide an effective sectional area as possible and as short an effective magnetic path as possible. In general, since a ferrite core having a larger outside diameter and a smaller inside diameter meets the above requirement, a ferrite core is selected for use which has an inside diameter that is as close to the dimensions of a flat cable to be used as possible.
However, there are many flat cables of various dimensions, and it is difficult to produce ferrite cores which can match those flat cables, respectively. Therefore, in reality, a ferrite core which is produced for use for a flat cable of certain dimensions is used for a flat cable which is smaller than the intended flat cable. In addition, there are some allowable tolerances in relation to the dimensions of ferrite cores; therefore, it is normal to select a ferrite core having a configuration in which a minimum value for the inside diameter of the ferrite core is larger than the dimensions of a flat cable which is put therethrough.
Thus, it is extremely difficult to select a ferrite core having an inside diameter which is extremely close to the dimensions of a flat cable, and it has been difficult to select a ferrite core that allows a flat cable which is used together to obtain an optimum impedance.
In order to solve the above-described problems, a first object of the present invention is to provide a noise preventing split ferrite core for a flat cable and a noise preventing component that are easy to be attached to, detached from and fixed to a flat cable and, therefore, which can be adapted to cope with flat cables of various dimensions to thereby eliminate noise in an effective fashion.
A second object of the present invention is to provide a wiring harness and an electronic apparatus in which a split ferrite core is attached to a flat cable which is easy to be attached to, detached from and fixed to a flat cable and therefore which can be adapted to cope with flat cables of various dimensions to thereby eliminate noise in an effective fashion.
Other objects and novel features of the present invention will be made apparent as modes of carrying out the present invention are described later.
With a view to attaining the above objects, a split ferrite core, especially for a noise prevention from a flat cable, according to the present invention comprises first and second split ferrite core bodies. The first split ferrite core body includes first and second leg portions, and the first leg portion is substatially vertical with respect to the second leg portion. The second split ferrite core body includes third and forth leg portions, and the third leg portion is substatially vertical with respect to the forth leg portion. The first leg portion of the first split ferrite core body abuts against the forth leg portion of second split ferrite core body, and the second leg portion of the first split ferrite core body abuts against the third leg portion of second split ferrite core body. With the above-mentioned construction of split ferrite core, a closed magnetic path is formed.
A noise preventing component according to the present invention comprises a split ferrite core and at least one fixing component. The split ferrite core includes first and second split ferrite core bodies. The first split ferrite core body includes first and second leg portions, and the first leg portion is substatially vertical with respect to the second leg portion. The second split ferrite core body includes third and forth leg portions, and the third leg portion is substatially vertical with respect to the forth leg portion. The first leg portion of the first split ferrite core body abuts against the forth leg portion of second split ferrite core body, and the second leg portion of the first split ferrite core body abuts against the third leg portion of second split ferrite core body. The fixing component holds the split ferrite core body assembled. With the above-mentioned construction of noise preventing component, a closed magnetic path is formed, and fixing components holds the split ferrite core in an assembled state.
A wiring harness according to the present invention comprises a flat cable, a split ferrite core and at least one fixing component. The split ferrite core surrounds said flat cable, and said split ferrite core includes first and second split ferrite core bodies. The first split ferrite core body includes first and second leg portions, and the first leg portion is substantially vertical with respect to the second leg portion. The second split ferrite core body includes third and forth leg portions, and the third leg portion is substantially vertical with respect to the forth leg portion. The first leg portion of the first split ferrite core body abuts against the forth leg portion of second split ferrite core body, and the second leg portion of the first split ferrite core body abuts against the third leg portion of second split ferrite core body. The fixing component holds the split ferrite core body together. With the above-mentioned construction of split ferrite core, a closed magnetic path is formed.
An electronic apparatus according to the present invention comprises a flat cable, a split ferrite core and at least one fixing component. The split ferrite core surrounds said flat cable, and said split ferrite core includes first and second split ferrite core bodies. The first split ferrite core body includes first and second leg portions, and the first leg portion is substantially vertical with respect to the second leg portion. The second split ferrite core body includes third and forth leg portions, and the third leg portion is substantially vertical with respect to the forth leg portion. The first leg portion of the first split ferrite core body abuts against the forth leg portion of second split ferrite core body, and the second leg portion of the first split ferrite core body abuts against the third leg portion of second split ferrite core body. The fixing component holds the split ferrite core body together. With the above-mentioned construction of split ferrite core, a closed magnetic path is formed.
In the present invention, the split ferrite core bodies are formed, for example, into a L-shape, respectively, and they are adapted to be assembled together so as to form a closed magnetic path. In this construction, inside diameters of the assembled ferrite core bodies can be changed in any fashion with respect to width and thickness directions of the flat cable, and therefore with a small variety of ferrite core configurations, it is possible to cope with flat cables of various widths and thicknesses.
Moreover, as described above, in general, it is believed that the impedance of a ferrite core is in proportion to the effective sectional area thereof and is in inverse proportion to the effective magnetic path thereof, but in the case of the split ferrite core bodies formed in L-shaped or the like, since the effective magnetic path thereof can be made shorter by narrowing the inside diameter of the ferrite core bodies in either the width or the thickness direction of the flat cable with the effective sectional area being kept constant, the impedance of the ferrite core bodies can be increased, whereby noise can effectively be eliminated from the flat cable.
In addition, according to the present invention, it is possible to provide the noise preventing component that can easily be attached to and/or detached from the flat cable by using the assembled split ferrite core bodies, for example, L-shaped, and the fixing components for fixing the assembled ferrite core bodies together.
Moreover, according to the present invention, the fixing components for fixing the split ferrite core bodies together can produce a force acting in the inside diameter direction of the assembled split ferrite core bodies, a force is in turn produced for allowing the split ferrite core bodies to hold the flat cable therebetween, thereby making it possible to fix the split ferrite core so attached to the flat cable to such an attached position. When comparing this construction with the construction in which an adhesive or an adhesive tape is used, the present invention can provide a better work efficiency.
Furthermore, the split ferrite core can be attached to and/or detached from the flat cable more easily by combing the noise preventing component with the closable case which can accommodate therein the split ferrite core. In addition, with the ferrite core being accommodated in the case, even if a direct impact is applied to the case, no direct impact is applied to the ferrite core, and therefore it is possible to prevent a damage to the ferrite core.
Moreover, irrespective of the construction of the case, there is provided a two-part case or an integral-type case comprising two case bodies which are connected to each other at a hinge portion, and in either of the two cases, the split ferrite core bodies, for example L-shaped, are accommodated, respectively, in the two case bodies. In addition, it is preferable to provide a pawl portion at a position where the split ferrite core body is accommodated for preventing the split ferrite core body from being detached therefrom. Also, it is preferable to provide a spring portion for obtaining a force with which the split ferrite core bodies hold the flat cable therebetween.
Irrespective of the material of the fixing component or the case for the ferrite core, a metal or a resin can be used as a material therefor. In addition, when used for the fixing component or the case, a material which has a certain degree of flexibility or elasticity can produce a force with which the split ferrite core bodies can hold the flat cable therebetween, and therefore it is preferable to use such a material for the fixing component or the case. Moreover, for the case, it is preferable to use a material, such as a resin in particular, that can absorb an impact applied thereto.
In the case of the ferrite core comprising the split ferrite core bodies which are combined with each other as described above, if it has dimensions allowing the core to cope with a flat cable of maximum dimensions, the ferrite core can cope with flat cables of dimensions smaller than the maximum ones. Due to this, when considering a manufacturer of ferrite cores, only a single configuration has to be prepared for a mold, which is for the ferrite core that can cope with the flat cable of maximum dimensions, this serving not only to reduce the production costs but also to facilitate the management of production.
Furthermore, with the wiring harness comprising the noise preventing split ferrite core or the noise preventing component for a flat cable according to the present invention in which the split ferrite core bodies, for example, L-shaped, are assembled together and a flat cable which is combined with the core or component, since a noise preventing means is provided in advance for the flat cable, the wiring harness can be installed in an electronic apparatus with good efficiency.
Moreover, with the electronic apparatus adopting the aforesaid noise preventing split ferrite core or noise preventing component and the flat cable combined with the core or component, the ferrite core can easily be attached to the flat cable, and since the ferrite core is fixed to the flat cable sufficiently securely, there is caused no risk of the ferrite core moving over the flat cable due to vibrations applied to the apparatus, thereby making it possible to secure a position where an optimum noise elimination can be effected.